Optical information processors using laser light are practically used in a variety of areas since these devices are high-speed and able to handle large amounts of information.
In these optical information processors, performance of light-beam deflectors is one of the most important factors to determine the performance of the optical information processors.
Heretofore, light-beam deflectors have been broadly classified into mechanical deflectors such as galvanometers, polygon mirrors, and hologram disks, and non-mechanical deflectors such as acoustooptic and electrooptic devices. The former is large in deviation and is thus practical, but is low in scanning speed and high-speed operation is limited, and, since it has mechanically operating portions and the optical system is complex in structure, the device tends to be large in size.
On the other hand, non-mechanical deflectors have no mechanical portions, can be controlled by optical or electrical signals, and a compact and high-speed device can be formed, and the following has been proposed.
For example, Japanese Patent Publication Laid-open 60-98422/1985 (U.S. Pat. No. 4,799,750), Japanese Patent Publication Laid-open 61-70533/1986 (U.S. Pat. No. 4,778,236, U.S. Pat. No. 4,886,587), Japanese Patent Publication Laid-open 59-192232/1984, and Japanese Patent Publication Laid-open 62-47627/1987 propose optical devices and light-beam deflectors which use acoustooptic effects or electrooptic effects to deflect light transmitting in a waveguide and output through a prism or grating, deflecting light in a plane parallel to a waveguide. However, these light-beam deflectors have problems of small deviation of only several degrees in a plane parallel to the waveguide. Japanese Patent Publication Laid-open 57-181529/1982 proposes a light-beam deflector which uses mode conversion by electrooptic effects and outputs through a prism or grating, thereby deflecting light in a plane perpendicular to the waveguide. However, since this deflector uses mode conversion, it has no continuity in deviation, and cannot be utilized in beam scanners and printers. Japanese Patent Publication Laid-open 58-125023/1983 (U.S. Pat. No. 4,762,383) proposes a two-dimensional light-beam deflector which uses acoustooptic effects to deflect guided wave in the waveguide plane and uses thermooptic effects to vary refractive index of the waveguide, thereby deflecting light in a direction perpendicular to the waveguide plane, and Japanese Patent Publication Laid-open 58-130327/1983 (U.S. Pat. No. 4,762,383) proposes a two-dimensional light-beam deflector which deflects light in a waveguide plane, and uses electrooptic effects to vary refractive index of an output grating, thereby deflecting the light in a direction perpendicular to the waveguide plane.
However, these light-beam deflectors use acoustooptic effects to deflect light in a plane parallel to the plane parallel to the waveguide, and, for the deflection in a direction perpendicular to the waveguide plane, the former uses thermooptic effects which provide a very small deviation and a slow response, and the latter uses electrooptic effects with a very small deviation. Thus, prior art non-mechanical light-beam deflectors have been very small in deviation, which makes it difficult to scan large areas, and have had no continuity in deviation, which is a problem with practical use.
Formerly, the inventors have proposed a non-mechanical light-beam deflector in Japanese Patent Publication Laid-open 1-132744/1989 which is provided in the waveguide with means for controlling the effective index and a grating for obtaining light from the waveguide with a deviation according to the effective index. However, this device has required a very large change in the effective index in order to obtain a deflection-angle range of 10.degree.-30.degree., and has thus required a thin film material having so high electrooptic effects that enable large changes in the effective index.
Normally, a light-beam deflector is required to have properties as follows:
Max. deviation: .theta..gtoreq.30.degree. PA1 Resolution: N(=.theta./.DELTA..theta.).gtoreq.1000 (wherein .DELTA..theta. is a beam spread angle) PA1 Deflection efficiency: .eta..gtoreq.30%
The scanning speed of light-beam deflector by an existing polygon mirror is about 10 kHz. However in view of high-speed operation requirements for optical information processors a scanning speed of 30 MHz or more is now required.
The inventors have conducted intensive investigations and completed a guided wave light-beam deflector having a large deviation, which does not require the use of a material having high electrooptic effects.